Catalyst composition for oxychlorination

ABSTRACT

The present invention relates to a catalyst composition for the oxychlorination of ethylene, comprising a mixture of metal salts on a support, where said metal salts are applied to the support in such ratios that the catalyst composition comprises a) from 3 to 12% by weight of copper as copper salt, b) from 0 to 3% by weight of an alkaline earth metal as alkaline earth metal salt, c) from 0 to 3% by weight of an alkaline metal as alkaline metal salt, d) from 0.001 to 0.1% by weight, preferably from 0.005 to 0.05% by weight, of at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium and platinum, and/or from 0.0001 to 0.1% by weight, preferably from 0.001 to 0.05% by weight, of gold, as corresponding metal salt or tetrachloroauric acid, where all percentages by weight are based on the total weight of the catalyst including support material. The invention further provides a process for preparing 1,2-dichloroethane by oxychlorination of ethylene in the presence of the above catalyst composition as catalyst.

The present invention relates to a catalyst composition for theoxychlorination of ethylene, comprising a mixture of metal salts on asupport, where said metal salts are applied to the support in suchratios that the catalyst composition comprises from 3 to 12% by weightof copper as copper salt, from 0 to 3% by weight of an alkaline earthmetal as alkaline earth metal salt, from 0 to 3% by weight of an alkalimetal as alkali metal salt, from 0.001 to 0.1% by weight, preferablyfrom 0.005 to 0.05% by weight, of at least one metal selected from thegroup consisting of ruthenium, rhodium, palladium, osmium, iridium andplatinum, and/or from 0.0001 to 0.1% by weight, preferably from 0.001 to0.05% by weight, of gold, as corresponding metal salt, also astetrachloroauric acid (HAuCl₄) in the case of gold, where allpercentages by weight are based on the total weight of the catalystincluding support material.

The invention further relates to a process for preparing1,2-dichloroethane by oxychlorination of ethylene, in which a mixture ofethylene, oxygen or oxygen-containing gas and hydrogen chloride isreacted by means of a catalyst of the above composition to form1,2-dichloroethane.

The oxychlorination of ethylene to form 1,2-dichloroethane is agenerally known process in which ethylene is reacted with hydrogenchloride and oxygen or with an oxygen-containing gas (e.g. air) in thegas phase and usually in the presence of a catalyst. Suitable catalystsgenerally comprise a copper compound as catalytically active componentdeposited on a support substance, preferably copper chloride on asupport substance.

Two process in particular have become established in industry, namely aprocess in which the catalyst is arranged as a fixed bed and a processin which the reaction is carried out in a moving bed.

Furthermore, it is known that the presence of copper chloride alone in acatalyst composition for the oxychlorination is disadvantageous, sincecopper chloride is volatile at the reaction temperatures customary inoxychlorination, which leads to a loss of catalyst effectiveness overtime. For this reason, the supported catalysts used usually containpromoters by means of which the effectiveness of catalytically activecopper chloride on support substances is improved. These promotersinclude alkali metal chlorides, in particular potassium chloride andcesium chloride, alkaline earth metal chlorides, in particular magnesiumchloride, or chlorides of the rare earth metals, in particular ceriumchloride. For example, it has long been known that copper chloride isless volatile when it is used together with potassium chloride or sodiumchloride.

Thus, EP-A 0 582 165 describes a catalyst composition comprising asupport on which an active metal composition comprising from 2 to 8% byweight of copper as copper chloride, from 0.2 to 2% by weight of analkali metal, from 0.01 to 9% by weight of a rare earth metal and from0.05 to 4% by weight of a metal of group IIA of the Periodic Table(alkaline earth metals) is present.

EP-A 0 375 202 discloses a catalyst composition for oxychlorination,comprising a mixture of metal chlorides on a support. The mixtureconsists essentially of a mixture of copper chloride, magnesium chlorideand potassium chloride in such ratios that the catalyst compositioncomprises from 3 to 9% by weight of copper, from 0.2 to 3% by weight ofmagnesium and from 0.2 to 3% by weight of potassium.

A similar catalytically active metal chloride composition on a supportfor the oxychlorination of ethylene, in which the metal chlorides areused in such ratios that the composition comprises from 3 to 9% byweight of copper, from 1 to 3% by weight of magnesium and from 0.01 to1% by weight of potassium, is disclosed in EP-A 0 657 212.

U.S. Pat. No. 4,446,249 describes a catalytically active composition fora moving-bed catalyst in which from 0.5 to 3% by weight of at least onemetal from the group consisting of potassium, lithium, rubidium, cesium,alkaline earth metals and rare earth metals or mixtures of theseelements are deposited on the support substance γ-Al₂O₃ before thecopper chloride is deposited. This is then followed by deposition of thecatalytically active copper chloride on the support particles. Due tothis application of the active metal components to the support substancein two steps, the catalyst particles produced by this method have lesstendency to adhere to one another. This property is particularlyadvantageous when the catalyst is used as a moving bed.

The selectivity in which the ethylene is converted in theoxychlorination reaction into the desired end product 1,2-dichloroethaneand not into the by-products which are usual in oxychlorination isgreatly dependent on the catalyst composition employed. Especially inthe case of reactions with a high ethylene conversion, too manyby-products are still obtained when using the catalyst compositionscustomary hitherto.

When used as moving-bed catalysts, the particles of the customarycompositions tend to stick together, which threatens the continuity ofthe reaction. For this reason, moving-bed catalysts for theoxychlorination of ethylene to 1,2-dichloroethane have to be optimizednot only in respect of activity and selectivity but also have to displaysticking-free fluidization behavior. It has been found that copper-richcatalysts have a greater tendency to stick together than low-coppercatalysts.

It is an object of the present invention to provide a catalystcomposition for the oxychlorination of ethylene whose use in theoxychlorination increases the conversion of the starting materialsethylene and hydrogen chloride compared to the use of the catalystcompositions customary hitherto without the selectivity for formation of1,2-dichloroethane being reduced and without the catalyst stickingtogether when used as a moving bed.

We have found that this object is achieved by a catalyst composition forthe oxychlorination of ethylene, comprising a mixture of metal salts ona support, where said metal salts are applied to the support in suchratios that the catalyst composition comprises

-   -   a) from 3 to 12% by weight of copper as copper salt,    -   b) from 0 to 3% by weight of an alkaline earth metal as alkaline        earth metal salt,    -   c) from 0 to 3% by weight of an alkaline metal as alkaline metal        salt,    -   d) from 0.001 to 0.1% by weight, preferably from 0.005 to 0.05%        by weight, of at least one metal selected from the group        consisting of ruthenium, rhodium, palladium, osmium, iridium and        platinum, and/or from 0.0001 to 0.1% by weight, preferably from        0.001 to 0.05% by weight, of gold, as corresponding metal salt        or tetrachloroauric acid,        where all percentages by weight are based on the total weight of        the catalyst including support material.

The presence of small amounts of a salt of the platinum metals, namelythe group consisting of ruthenium, rhodium, palladium, osmium, iridiumand platinum, or the presence of small amounts of appropriate goldcompounds in the catalyst composition used increase the conversion ofthe starting materials ethylene and hydrogen chloride substantiallywithout reducing the selectivity for the formation of1,2-dichloroethane. As a result, a higher yield of 1,2-dichloroethane isobtained. When the catalyst is used as a moving bed, the fluidizationbehavior is not influenced by the addition of small amounts of theabovementioned metal salts. Metal salts of the platinum metals or ofgold used in this process are preferably the corresponding oxyhalides,the oxides or the halides of the platinum metals or of gold, inparticular the chlorides of the platinum metals or of gold.

The presence of a ruthenium salt, in particular the presence ofruthenium chloride, in the above-defined ratio in the catalystcomposition is also preferred.

Particular preference is given to the presence of a gold salt, inparticular gold chloride or tetrachloroauric acid, in the above-definedratio in the catalyst composition.

When the catalyst compositions which have hitherto been customary areused in the oxychlorination, ethane, water, traces of hydrogen chlorideand also chlorinated organic by-products plus carbon monoxide and carbondioxide are formed as by-products. CO and CO₂ are present in a ratio ofabout 1:1. In circulation reactor processes, after removal of the mainproduct 1,2-dichloroethane from the product gas stream, some of theseby-products of the oxychlorination are condensed out and some areusually discharged from the process via a purge stream. The remainingproduct gas which comprises as yet unreacted starting material, inparticular ethylene, is subsequently recirculated to the reactor.However, removal of by-products via a purge stream also results in smalllosses of 1,2-dichloroethane, the main product. Avoiding formation of COcould offer advantages in the work-up of offgas or recycle gas streams,since CO₂ can be scrubbed out more readily than CO.

The use of a catalyst composition according to the present invention inthe oxychlorination therefore offers not only the advantage of anincrease in the yield of 1,2-dichloroethane when a promoter from thegroup consisting of the platinum metals is used but also the furtheradvantage that only very small amounts of carbon monoxide are formedwhile carbon dioxide is formed as virtually exclusive by-product.

As support substance for the catalyst composition of the presentinvention, it is possible to use aluminum oxide, silica gel, pumice andclay. Preference is given to using aluminum oxide as support substance.The specific surface area of the support substance before deposition ofthe metal salt is preferably in the range from 20 to 400 m²/g, morepreferably from 75 to 200 m²/g. Customary support substances foroxychlorination catalysts preferably have a pore volume in the rangefrom 0.15 to 0.75 cm³/g, and the average particle sizes are preferablyin the range from 30 to 500 μm. In the support substances used here, theproportion of particles having a diameter of less than 45 μm is 30% or5%, with the BET surface areas being 170 m²/g or 150 m²/g.

The invention further provides a process for preparing1,2-dichloroethane by oxychlorination of ethylene in the presence of acatalyst composition according to the present invention as catalyst.

The process of the present invention for preparing 1,2-dichloroethanecan be carried out using the known techniques and reaction conditionswhich are generally customary according to the prior art. Ethylene,hydrogen chloride and molecular oxygen in the gas phase are brought intocontact with a catalyst composition according to the present inventionat from 80 to 300° C., preferably from 210 to 260° C. The molecularoxygen can be introduced as such or in the form of an oxygen-containinggas mixture, e.g. air. In the case of circulation reactor processes (gasrecycle mode) in which unreacted starting material is recirculated tothe reactor, only pure oxygen is used.

The molar ratios of the starting materials used in the process of thepresent invention are generally from 5:1 to 3:1, preferably about 4:1,for hydrogen chloride:oxygen and generally about 1:2 forethylene:hydrogen chloride. The hydrogen chloride is preferably presentin a slightly substoichiometric amount based on the reaction 2 C₂H₄+4HCl+O₂→2 C₂H₄Cl₂+2 H₂O, so that it is ensured that hydrogen chloride isvirtually completely reacted in one pass through the reactor. In the gasrecycle mode, ethylene is fed in in a still higher excess. Theethylene:HCl:O₂ ratio is preferably chosen so that ethylene, too, isvery substantially reacted in one pass through the reactor. The reactionpressure is in the range from 1 to 20 bar, preferably from 1 to 8 bar.

The material of construction used for the reactor is usually based oniron (stainless steel) or a nickel alloy. When an oxychlorinationreaction is carried out on a small scale, glass can also be used asreactor material.

In the process of the present invention, the catalyst can be used eitheras a fixed bed or as a moving bed. If the catalyst is used as a movingbed in the process of the present invention, it is preferably in afluidized state. This is generally achieved at velocities in the rangefrom 1 to 100 cm/s. If the catalyst is used as a fixed bed in theprocess of the present invention, it is preferably used in the form ofhollow cylinders or annular pellets whose end faces are rounded both onthe outer edge and on the edge of the central holes. This preferred formof fixed-bed catalyst can be made up of either hollow cylinders orannular pellets composed of catalytically active material or preferablysupport material in the shape of hollow cylinders or annular pellets towhich a catalytically active composition has been applied. The externaldiameter of the catalyst hollow cylinders or annular pellets is from 3to 20 mm, preferably from 3 to 10 mm, particularly preferably from 3 to7 mm, in particular from 3.5 to 6.5 mm, and the internal diameter isfrom 0.1 to 0.7 times the external diameter. The length of the catalysthollow cylinders or annular pellets is from 0.2 to 2 times, preferablyfrom 0.3 to 1.8 times, particularly preferably from 0.4 to 1.6 times,the external diameter. The radius of curvature of the end faces is from0.01 to 0.5 times, preferably from 0.05 to 0.4 times, particularlypreferably from 0.1 to 0.2 times, the external diameter. These catalystshapes, which are described in EP 1 127 618 A1, give a particularly lowpressure drop and display good mechanical strength and are particularlysuitable for use in strongly exothermic reactions such as theoxychlorination of ethylene.

Fixed-bed catalysts having a shape as described in EP 1 127 618 A1 arethus an integral part of the present invention and are incorporated byreference.

The invention further provides a catalyst for preparing1,2-dichloroethane by oxychlorination of ethylene in the presence of afixed-bed catalyst having a composition according to the presentinvention and, if desired, a shape as described in EP 1 127 618 A1.

To prepare an aqueous solution for impregnating the support substance,the required amounts of the appropriate metal compounds, preferably inthe form of their hydrates, are dissolved in water. The aqueous solutionis then applied to the support substance. The support substance whichhas been impregnated in this way is subsequently filtered off from theremaining aqueous phase if necessary and finally dried. Filtration isnot necessary when the support substance is brought into contact with avolume of the aqueous solution which is no greater than that sufficientfor saturating the support substance.

The present invention is illustrated by the following examples.

EXAMPLE 1

A catalyst composition according to the present invention was producedby impregnating the support substance with an aqueous solution obtainedas follows:

86.4 g of CuCl*2H₂O, 89.8 g of MgCl*6H₂O, 5.5 g of KCl and 0.2 g ofRuCl₃*H₂O were dissolved in a small amount of water. Further water wasadded until a total volume of 300 ml, corresponding to the maximum waterabsorption capacity of the amount of support substance used, wasobtained. This metal chloride solution was added to 600 g of an aluminumoxide support having a proportion of particles smaller than 45 μm of 30%and a BET surface area of 170 m²/g. After stirring for one hour, themixture was dried at 110° C. for 16 hours in the presence of nitrogen togive a catalyst A containing 4.5% by weight of Cu, 1.5% by weight of Mg,0.4% by weight of K and 0.01% by weight of Ru.

For comparison, a catalyst composition having the same proportions byweight of copper chloride, magnesium chloride and potassium chloride butwithout ruthenium chloride was produced in the same way (catalyst B).

Both oxychlorination catalysts (catalyst A and B) were installed in amoving-bed reactor made of glass into which the starting materialsethylene, air and hydrogen chloride were fed and which was maintained ata bed temperature of 232° C., 243° C. or 254° C. The reactor wasoperated at a pressure of 4 bar using an amount of 500 g of the catalystof the appropriate composition. In each case, 119 standard l/h of air,69.9 standard l/h of hydrogen chloride and 35.5 standard l/h of ethylenewere fed to the reactor, which gave a space velocity of 160 g ofcat./(mol of HCl h-1). The products formed in each case were analyzed bymeans of gas chromatography.

The results are collated in the table below.

Comparison of the results shows that the presence of small amounts ofruthenium chloride in the catalyst composition used increases theconversion of both hydrogen chloride and ethylene at the variousreaction temperatures without reducing the selectivity to1,2-dichloroethane (see table below). This is reflected in a significantincrease in the yield of 1,2-dichloroethane when using the catalystcomposition of the present invention (here catalyst A).

In addition, the results show that the formation of carbon monoxide asby-product is suppressed effectively when using the catalyst compositionof the present invention.

EXAMPLE 2

A further catalyst composition according to the present invention wasproduced in a manner similar to example 1 but using palladium chlorideas promoter instead of ruthenium chloride to give catalyst C containing4.5% by weight of Cu, 1.5% by weight of Mg, 0.4% by weight of K and0.01% by weight of Pd.

The results are collated in the table below. They clearly show theeffect of palladium, which is comparable to that of ruthenium both inrespect of the increase in activity and also in respect of thesuppression of CO formation.

EXAMPLE 3

A further catalyst composition according to the present invention wasproduced in a manner similar to example 1 but using gold chloride aspromoter instead of ruthenium chloride to give catalyst D containing4.5% by weight of Cu, 1.5% by weight of Mg, 0.4% by weight of K and0.005% by weight of Au.

The results are collated in the table below. They clearly show theeffect of gold, which increases the activity to a greater extent than doruthenium and palladium, particularly at the two lower temperatures.TABLE HCl Ethylene EDC EDC CO CO₂ Selectivity to formation of Temp.conversion conversion selectivity yield selectivity selectivitychlorinated by-products Catalyst (° C.) (%) (%) (%) (%) (%) (%) (total,%) A 254 98.93 98.54 95.87 94.47 0.07 2.17 1.88 A 243 97.42 96.48 97.4193.98 0.06 1.22 1.31 A 232 93.41 91.97 98.26 90.37 0.03 0.51 1.20 B 25497.90 97.42 96.08 93.60 1.04 1.00 1.88 B 243 95.18 94.37 97.41 91.930.84 0.52 1.22 B 232 89.19 88.21 98.55 86.94 0.53 0.23 0.68 C 254 98.8198.71 95.78 94.55 0.13 2.32 1.77 C 243 97.60 97.11 97.27 94.46 0.29 1.361.08 C 232 96.21 94.34 97.86 92.32 0.19 0.80 1.15 D 254 99.54 99.0295.22 94.28 1.04 1.32 2.43 D 243 98.82 98.00 97.26 95.31 0.69 0.77 1.27D 232 96.68 95.90 98.28 94.25 0.49 0.53 0.69

1-15. (Canceled)
 16. A catalyst composition for the oxychlorination ofethylene, comprising a mixture of metal salts on a support, wherein saidmetal salts are applied to the support in such ratios that the catalystcomposition comprises a) from 3 to 12% by weight of copper as coppersalt, b) from 0 to 3% by weight of an alkaline earth metal as alkalineearth metal salt, c) from 0 to 3% by weight of an alkali metal as alkalimetal salt, d) from 0.001 to 0.1% by weight of at least one metalselected from the group consisting of ruthenium, rhodium, palladium,osmium, iridium and platinum, and/or from 0.0001 to 0.1% by weight ofgold, as corresponding metal salt or tetrachloroauric acid, and whereinall percentages by weight are based on the total weight of the catalystincluding support material.
 17. The catalyst composition as claimed inclaim 16, wherein the metal salts are selected from metal halides, metaloxyhalides or metal oxides of the respective metal and tetrachloroauricacid.
 18. The catalyst composition as claimed in claim 17, wherein themetal halides are metal chlorides of the respective metal.
 19. Thecatalyst composition as claimed in claim 16, comprising from 0.005 to0.05% by weight of at least one metal selected from the group consistingof ruthenium, rhodium, palladium, osmium, iridium and platinum.
 20. Thecatalyst composition as claimed in claim 16, comprising from 0.001 to0.05% by weight of gold.
 21. The catalyst composition as claimed inclaim 16, wherein the component d) used, is a ruthenium salt or a goldsalt.
 22. The catalyst composition as claimed in claim 16, wherein thecomponent b) used, is a magnesium salt.
 23. The catalyst composition asclaimed in claim 16, wherein the component c) used, is a potassium salt.24. The catalyst composition as claimed in claim 16, wherein the supportused, is aluminum oxide.
 25. The catalyst composition as claimed inclaim 16, wherein the support has a pore volume in the range from 0.15to 0.75 cm³/g.
 26. The catalyst composition as claimed in claim 16,wherein the specific surface area of the support used, is in the rangefrom 20 to 400 m²/g.
 27. A fixed-bed catalyst comprising the catalystcomposition as claimed in claim 16, in the shape of hollow cylinders orannular pellets whose end faces are rounded both to the outer edge andto the edge of the central holes.
 28. A process for preparing1,2-dichloroethane, comprising oxychlorinating ethylene in the presenceof a catalyst composition as claimed in claim
 16. 29. The process asclaimed in claim 28, which is a circulation reactor process.
 30. Theprocess as claimed in claim 28, wherein the catalyst is used as a movingbed.
 31. The process as claimed in claim 28, wherein the catalyst isused as a fixed bed.
 32. The process as claimed in claim 31, wherein thecatalyst is used as a fixed bed in the form of hollow cylinders orannular pellets whose end faces are rounded both to the outer edge andto the central holes.